This invention relates to a safety system for railways using intensity of current which provides almost complete protection from the possibility of collision while it allows a high level of rail traffic with an optimum coefficient of line utilization.
It is known that until now, for reasons of safety, the distance between trains travelling on the same rails could be measured by eye, time or space. The first measurement, entrusted to the driver, is only used in exceptional circumstances and at extremely low speeds. Time distancing, based on the departure of trains at fixed intervals does not guarantee against the danger of collision and has therefore to be integrated with other regulations, leading in any case to a rather low theoretical line capacity.
The so-called space distancing calls for suddivision of the line into sections marked off by signals, each of which can be occupied by a single train after it has been left free by the train immediately preceding it. The control of the freeing of a section can be carried out by a person or mechanically, using, for example a pair of axle-counter devices which compare the number of axles of a train as this enters and leaves a section, allowing a train to enter the section after this control. Automatic blocking systems also exist in which signals showing the track to be occupied are controlled from the trains by means of so-called "track circuits".
It is also known that all these safety systems are not entirely satisfactory because although they do not permit the optimum usage of the track they are notably expensive.
It should also be noted that the above methods apply to lines with double tracks each of which is occupied by trains going in the same direction, while on single track lines, where the same track is used for trains going in opposite directions, only by distancing can safety be guaranteed, obviously slowing down circulation even further.